Pressure-sensitive release and adhesive materials are well known and in wide commercial use to secure tapes, labels, or other articles to receiving surfaces. Such adhesives can be attached to a variety of materials by the simple application of pressure. Thus tapes coated with adhesive on opposite sides are used to join two articles together.
Pressure-sensitive adhesives are generally based on elastomeric polymers including natural and synthetic rubbers. They can be compounded with extenders, plasticizers, tackifiers and other materials to provide specifically desired properties. Examples of such materials and their use are provided in numerous prior art U.S. patents, including U.S. Pat. Nos. 3,085,903; 3,246,049; 3,356,635; 3,501,365; and 3,532,652.
Because such adhesives are tacky, it is customary to cover their exposed surfaces temporarily, and removably, with a release layer, typically a nontacky silicone polymer. This facilitates handling, storage and dispensing. The resulting products include label stock in which a base or support is bonded to the adhesive and the exposed adhesive surface is covered with a silicone-release paper or film. Another example is a spirally wound tape with a film or paper support having one surface bonded to an adhesive. The exposed adhesive surface is in contact with a release layer that is carried by the opposite side of the support, or by a separate interleaving support. Still another example is a spirally wound transfer tape in which the support is coated on both sides with release layers, and one of the release layers is overcoated with adhesive. The adhesive initially can be formed directly on the support surface, or on the release surface. The latter is necessary for transfer tapes with release coatings on both sides of the support. Consistently low uniform release forces between the adhesive and release layer are more difficult to obtain when the adhesive is solidified from a liquid in contact with the release layer surface.
The foregoing structures are "laminates" which are composite structures having at least one support, temporary or permanent, a pressure-sensitive adhesive layer, and at least one release layer in surface contact with the adhesive. Other layers such as a second release layer or a second support may also be present.
Elastomeric, pressure-sensitive silicone adhesives are widely known and have a number of attractive properties. They are useful over a wide range of temperatures, both high and low; they are chemically stable, and have good adhesion to a variety of materials. However, silicone pressure-sensitive adhesives adhere with such tenacity to conventional release surfaces, that the materials often tear before releasing. The consequence is that the use of silicone adhesive has been limited generally to direct application without a release layer, or to use with plastic films strong enough to withstand the considerable release forces required in unwinding spiral tapes. Release surfaces with ridges which tend to reduce contact area have also been employed with limited success, but at increased expense.
Accordingly, an object of the invention is to realize a silicone pressure-sensitive release laminate that is practical for use, both immediately after preparation and after extended periods of storage.
Another object is to realize silicone adhesive laminate structures which can be releasably separated with stripping or release forces comparable with known, nonsilicone pressure-sensitive adhesive laminates.
Still another object is to realize silicone pressure-sensitive laminate structures which permit the use of existing pressure-sensitive application techniques and equipment.
A further object of the invention is to facilitate the use of silicone adhesives. A related object is to provide release materials for such adhesives which expedite their use.
Still another object is to achieve release and adhesive combinations which are readily produced and are usable over a wide range of temperature conditions. A related object is to achieve a silicone release and adhesive laminate which is operable under frigid Arctic conditions, as well as humid and high temperature tropical conditions.